Summary
Summary Module 2.5: Biological membranes
- Institution
- OCR
OCR A level biology Key concepts including cell membranes and transport
[Show more]
Seller
Follow
Content preview
BIOLOGICAL MEMBRANES Cell membrane receptors1) Specific shape – only complimentary can bind
Role of membranes 2) Cell that responds = target cell
- Site of chemical reactions + cytoskeleton attach 3) Membrane bound receptors
- Cell signalling 4) Drugs also bind + trigger response / block
- Compartmentalisation = partially permeable
membranes allow specific conditions for reactions Factors affecting permeability
Changing solvent
Fluid mosaic model - Organic solvents dissolve mem (alcohol, less polar)
- Pure alcohols destroy cells (bacteria), ethanol
dissolves lipids in mem, lose struc, ↑ permeability
- Nonpolar (benzene) enter membrane + disrupts
Temperature
Phospholipids ↓ kinetic energy so not move
Packed closely = rigid
<0
ATP production slows
Ice crystals may pierce membrane
Phospholipids fluid, partially permeable
0-45
Phospholipids ↑ temp ↑ kinetic energy ↑ permeability
- 7nm thick, free to move Bilayer melts, fluid, ↑ permeability
- Hydrophilic head interact with water 45 < Water inside expands
Proteins denature ↑ permeability
- Hydrophobic tail (amphipathic) form core
- Arrange into bilayer with hydrophobic core
- Barrier to water soluble subst, fat soluble diffuse Beetroot contains pigment betalain
Change method by using different solvents
Intrinsic proteins 1) Cut 5 pieces of beetroot using cork borer, rinse + dry
- Transmembrane proteins, scattered / embedded 2) Place in indifferent test tubes, 5cm3 distilled water
- Aa with hydrophobic r group interact hphobic core 3) Place water baths at diff temps for same time
- Channel protein – hphilic channel, polar moleules, 4) Remove beetroot, filter liquid into cuvette
specific molecules, passive down conc gradient 5) Use colorimeter on blue light (↑ permeability, more
- Carrier protein – move ions, protein changes shape, pigment released, higher absorption)
facilitated diffusion + AT
Transport across membrane
Extrinsic proteins (peripheral) Diffusion
- Hphilic R groups interact with polar phosphate heads - Passive process
- Specific position for chemical reaction to take place - Net movement from area of high conc to low conc
(down conc gradient) until equilibrium
Glycoproteins - Rate – conc difference, mem thickness, SA, temp
- Intrinsic proteins with carbohydrate chain - Partially permeable – small, non-polar, fat soluble
- Stabilise membrane = H bonds with water diffuse between phospholipids (o2, co2), polar diffuse
- Cell adhesion + receptors for chemical signals through membrane at slow rate (water + urea)
- Neurotransmitters/drugs bind + prevent/tigger resp
Facilitated diffusion = through carrier + channel proteins
Glycolipids - Passive process
- Lipids with carbohydrate chain - Selectively permeable membrane
- Cell marker/antigen = immune system recognises - Channel proteins for polar molecules + ions
- Glycocalyx = membrane cover for recognition - Carrier proteins only down conc gradient
- Rate affected by number of proteins present
Cholesterol
- Lipid, hydrophilic end and hydrophobic end Diffusion into model cells
- Binds to phospholipid hydrophobic tail = pack close Variation: SA in same conc, different conc + equal size,
- ↓ fluid ↑ rigid, not too solid same size in different temps
1) Agar cubes diff sizes, phenolphthalein (pink in alkali)
Cell signalling = comms responds to change (cascade) 2) Fill beaker with sodium hydroxide + insert cubes
1) Cell released messenger molecule (hormone) 3) Record the time for each cube to turn pink
2) Travels to target cell + bind to receptor on mem 4) Calculate rate of diffusion
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller katieg1500. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £5.00. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
73918 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy revision notes and other study material for 14 years now